In the mid-1990s, after the collapse of the Soviet Union, North Korea invited the Makeyev Design Bureau's ballistic missile designers and engineers to develop this missile, based on the R-27 Zyb.
It was decided that, as the Korean People's Army's MAZ-547A/MAZ-7916 Transporter erector launcher could carry 20 tonnes, and the R-27 Zyb was only 14.2 tonnes, the R-27 Zyb's fuel/oxidizer tank could be extended by approximately 2 metres. Additionally, the warhead was reduced from a three-warhead MIRV to a single warhead.
The actual rocket design is a liquid fuel rocket, generally believed to use a hypergolic combination of unsymmetrical dimethylhydrazine (UDMH) as fuel, and nitrogen tetroxide (NTO) as oxidizer. Once the fuel/oxidizer combination are fed into the missile, it could maintain a 'ready to launch' condition for several days, or even weeks, like the R-27 SLBM, in moderate ambient temperatures. A fueled Musudan would not have the structural strength to be land transported, so would have to be fueled at the launch site.
It was originally believed that Musudan's rocket motors made up the second stage of the Taepodong-2, which North Korea unsuccessfully test fired in 2006. However analysis of the Unha-3 launch, believed to be based on the Taepodong-2, showed that the second stage did not use the same fuel as the R-27, and is probably based on Nodong rocket technology. There is a possibility that the Musudan likewise is using the Nodong's kerosene and corrosion inhibited red fuming nitric acid (IRFNA) propellants, reducing the missile's range by about half.